import math
x1,y1,x2,y2=map(float,input().split())


print(round(math.sqrt((x1-x2)**2+(y1-y2)**2),7))
 import math math x1,y1,x2,y2=map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 print(round(math.sqrt((x1-x2)**2+(y1-y2)**2),7)) print round(math.sqrt((x1-x2)**2+(y1-y2)**2),7) round math.sqrt((x1-x2)**2+(y1-y2)**2) math.sqrt math sqrt (x1-x2)**2+(y1-y2)**2 (x1-x2)**2 x1-x2 x1 x2 2 (y1-y2)**2 y1-y2 y1 y2 2 7 x2,y2=map(float,input().split()) map(float,input().split()) x2 y2=map(float,input().split()) map(float,input().split()) y2 x1,y1,x2,y2=map(float,input().split()) map(float,input().split()) x1 y1,x2,y2=map(float,input().split()) map(float,input().split()) y1
import math
x1,y1,x2,y2=map(float,input().split())


print(round(math.sqrt((x1-x2)**2+(y1-y2)**2),7))

